Virtually nothing is known about the frequency of "null" allozyme alleles (alleles which code for the production of no enzyme activity) in natural populations or their importance to the well-being of the individuals which carry such alleles. This study seeks to answer these questions for several natural populations of Drosophila melanogaster. BIBLIOGRAPHIC REFERENCES: Voelker, R.A., and Langley, C.H. (1977) Cytological localization of Roi (rough eye). Drosophila Information Service 52.